1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same. More particularly, the invention relates to a technique of using a low dielectric-constant insulating film as an interlayer insulating film.
2. Description of the Related Art
It is proposed that insulating films having lower relative dielectric constants than ordinary SiO2 films be used as interlayer insulating films in LSIs. The use of low dielectric-constant insulating films can lower inter-wiring capacitances, making it possible to enhance the operating speed of the LSI.
Most low dielectric-constant insulating films are, however, softer and more fragile than ordinary SiO2 films. They are likely to be deformed, scratched or cracked. When used as interlayer insulating films in any LSI, too, they may be deformed or cracked when pads are connected to an external portion, inevitably decreasing the reliability or yield of the LSI. More specifically, they may be deformed or cracked when they receive a pressure as a test probe pressed onto the pads to evaluate the characteristics of LSI elements or as wire bonding is performed to connect the pads to an external portion.
To solve this problem, an insulating film made of ordinary SiO2 may be formed in the peripheral region of a semiconductor chip, where the pads are provided, and a low dielectric-constant interlayer insulating film may be formed in the circuit region inside the peripheral region, where transistors, wires and the like are provided.
Pads are formed on the interlayer insulating films that lie, one above another, in the peripheral region of the chip. The pads formed on each interlayer insulating film are connected to the pads formed on the next interlayer insulating film by conductive portions (vias) that extend through the interlayer insulating film. To provide this structure, the following sequence of steps must be performed for each layer of the chip.
First, a low dielectric-constant insulating film is formed on the entire surface. Next, a peripheral part of the insulating film is removed. Then, an SiO2 insulating film is formed in the removed region. Further, a via and a pad are formed. Obviously, many steps must be performed to manufacture the semiconductor device. This inevitably decreases the productivity.
As described above, low dielectric-constant interlayer insulating films are soft and fragile and likely to be deformed or cracked when pads are connected to the external portion. If deformed or cracked, they will degrade the reliability and characteristics of the device. To prevent the reliability and characteristics of the device from being degraded, it is proposed that an ordinary insulating film, such as SiO2 film, be formed in only the peripheral region of the chip, where pads are provided. Since pads and conductive portions are formed at each layer, however, many steps must be performed to manufacture the semiconductor device. This inevitably decreases the efficiency of manufacturing the semiconductor device.